1. Field of the Invention
The invention relates to a method of and apparatus for testing materials, such as microbiological growth control agents for paper mill streams or cooling waters, or waste intended for biological treatment to determine whether or not such materials are effective in inhibiting or preventing growth of microorganisms. The method and apparatus of this invention directly compare the actual effect of a sample of the waste on the growth of microorganisms as measured by the turbidity or lack of same in liquid mediums containing them. In the present invention, turbidity indicates growth whereas clearness or lack of turbidity indicates the presence of materials inhibitory or toxic to the growth of microorganisms. The present invention also provides means for ensuring against false microorganism growth indications because of turbidity from precipitates which might form from possible reaction of the test sample of waste with one or more components of the medium or which might form from any of components of the medium or inter-reaction of two or more such components.
2. Description of the Prior Art
Biological waste treatment involves the oxidation of chemical compounds by active microorganisms to innocuous end products. Both the rate and the extent of oxidation are dependent upon the "health" of the microorganisms and the various characteristics of the influent waste. A common method for treating sewage to remove pollutants is by the activated sludge process. According to this process, the sewage, with or without primary clarification, is thoroughly mixed with oxygen-containing gas in the presence of aerobic bacteria in a lagoon of active microorganisms commonly called a secondary treatment lagoon. The organic matter contained in the sewage is absorbed and biologically oxidized by the bacteria. Subsequently, the bacteria are separated, e.g., by gravity settling, the purified effluent is decanted and discharged into a receiving stream or body of water with or without prior disinfection with chlorine or ozone.
The problems encountered in treating industrial wastes are more complex, especially in the secondary treatment, than with domestic wastes. Some synthetic industrial compounds produced by or used in process units are inhibitory to the respiration of the biological microorganisms in the secondary waste treatment unit. Therefore, the detection of the presence of potentially inhibitory or toxic materials in the waste before the waste reaches the secondary unit is preferred to protect the microorganisms in the secondary treatment units from large concentrations of highly toxic materials. Control of these potential upsets is required to avoid severe damage to the secondary treatment lagoon, to avoid pollution of the stream or body of water receiving the effluent from the secondary treatment lagoon, and so that the treatment plant can conform to public waterway discharge permits. Inhibitory materials can be low to high concentrations of potentially toxic compounds. In the case of inhibitory or toxic compounds, a percentage of the biological organisms may be killed or inhibited, thus reducing the efficiency of the secondary biological waste treatment or even rendering it ineffective.
In order to effectively treat a waste biologically a number of its characteristics must be known. Among these characteristics is the presence of materials that affect biological growth, e.g., toxic componds. Often a waste that is toxic can be treated by the application of a detoxification step prior to biological treatment. Another approach is to eliminate the toxicant at its source and treat by an alternative means. A very integral part of any study related to toxicity, be it detoxification or point source identification, is the toxicity evaluation test. The purpose of the toxicity evaluation test is to ascertain a material's toxic impact on the biomass (microorganisms).
Most biomass toxicity tests in current use in regard to water pollution control processes, are based on a measurement of the biological oxygen consumption. Such tests have proven to be insensitive in some cases, because, although a particular biomass may not be capable of growth, it can still show an oxygen uptake. This is apparently true since oxygen uptake measurements are taken over periods of time where growth may not necessarily be the result of oxygen consumption. In any event, the real question of toxicity, with respect to biological treatment, should be whether the biological system will sustain growth rather than will it show an oxygen uptake.
Furthermore, previous attempts to protect the secondary treatment unit took the form of BOD detection systems inside the primary or secondary treatment boundaries. As a consequence, any abnormal influent waste conditions were detected too late in many cases for correction or diversion. Commercially available oxygen uptake monitors are typically installed in the biobasin and measure the respiration of the biomass after influent waste water has been pumped into the aerobic biological basin. No really effective positive corrective measures can be initiated at this point and it is usually too late to avoid damage and loss. Examples of prior art which measure the respiration of the biomass after the influent waste water has been pumped into the aerobic biological basin include U.S. Pat. Nos. 3,342,727; 3,348,409; 3,426,899; 3,510,407; 3,557,954; 3,731,522 and 3,740,320. U.S. Pat. No. 3,684,702 describes a laboratory technique for determining toxic sewage waters wherein one analysis fermenter is continually supplied with sewage water, bacteria and additional nutrient while a second analysis fermenter contains only bacteria and the additional nutrient. if the oxygen consumption per time unit is smaller in the first fermenter than in the second, an impediment or poisoning of the bacteria is stated to exist, as a result of which alarms are sounded or countermeasures are taken. However, the waste water is already at the secondary unit leaving essentially no time for corrective measures and it is not always accurate to assume that the oxygen uptake results from biological growth.
Other prior art such as U.S. Pat. Nos. 2,990,339; 3,014,848; 3,255,095; 3,474,001; 3,504,185; 3,714,445; 3,730,842; and 3,832,532 illustrate the well known expedient of measuring turbidity, optical density or light scattering ability as indicators of microorganism population. None of the patents mentioned above, however, disclose or suggest the incubating on a porous inert support mass of a mixture of a sample of the material being tested with a liquid medium containing microorganisms and capable of supporting growth of the microorganisms, removing and filtering the mixture and observing its turbidity.
Furthermore, no prior art is known which discloses, teaches or suggests a method of or apparatus for measuring the actual effect of industrial sewage or other liquid waste on the health, vigor or growth potential of microorganisms in the manner described herein.